EXPERIMENTAL AND CLINICAL INVESTIGATIONS OF THERMAL WASHOUT METHOD FOR MEASURING THE RIGHT VENTRICULAR EJECTION FRACTION

Abstract

Measurement of right ventricular ejection fraction and right ventricular end-diastolic volume is important for evaluation of right ventricular function, however, the anatomical characteristics of the right ventricle have made clinical assessment difficult. The purpose of this investigation was to determine whether a modified Swan-Ganz catheter equipped with a rapid response thermistor could detect temperature change in the model heart to identify clinical problems occurring when right ventricular ejection fractions in ICU patients were measured by this method, and to determine whether problems encountered in clinical application were able to be analyzed in the model heart. Use of a commercially-available Swan-Ganz catheter equipped with a rapid response thermistor enabled analysis of the ventricular ejection fraction and ventricular end-diastolic volume without any time delay compared to measurements calculated from the impedance change in the model circuit which was composed of a peristaltic, artificial pump (Stakart, Cobe, USA) and artificial chamber. Next two hundred and sixty-eight records of right ventricular thermal washout curves from fifteen patients, who admitted to the ICU of Gurima University Hospital and were monitored using Swan-Ganz catheter equipped with rapid response thermistor were analyzed. From the clinical analysis two questions were proposed. The first considered why successive ejection fractions obtained from a single thermal washout curve were not always identical, and the the second considered why the difference among ejection fractions became apparent especially when the measured ejection fractions was high. To determine answers to these questions, an artificial heart was developed equipped with two one-way valves and a rubber base connected to a piston. We determined in this model heart that the injection port of the cold indicator had to be the ventricle; the cooled catheter and possibly the ventricle made successive ejection fractions decrease when the preset ejection fraction was high; the ejection fraction was calculated to be about 30% less than the actual one when cold water was injected in the atrium through a catheter running in the inflow tract; and that the ejection fraction in a thermal washout curve obtained first was the most accurate when cold water was injected in the ventricle. These results were good agreement with clinical findings. In conclusion, the ejection fraction in a thermal washout curve obtained first from right ventricular injection should be adopted when analyzing right ventricular ejection fraction by thermal washout method.